FOX, Fltk, and other specialty GUI toolkits

From Unix Insider: "Why are there so many GUI toolkits? Who's using all of those non-mainstream libraries? Last year,
Cameron Laird and Kathryn Soraiz profiled the leading GUI toolkits for general Unix development: Motif,
Tk, Qt, GTK+, and wxWindows. Now they round up the alternatives and summarize the state of their art."